1. Field of the Disclosure
The present disclosure relates generally to electrophotographic image forming devices, and more particularly to an overcoat layer for an organic photoconductor drum having excellent abrasion resistance and electrical properties.
2. Description of the Related Art
Organic photoconductor drums have generally replaced inorganic photoconductor drums in electrophotographic image forming device including copiers, facsimiles and laser printers due to their superior performance and numerous advantages compared to inorganic photoconductors. These advantages include improved optical properties such as having a wide range of light absorbing wavelengths, improved electrical properties such as having high sensitivity and stable chargeability, availability of materials, good manufacturability, low cost, and low toxicity.
While the above enumerated performance and advantages exhibited by an organic photoconductor drums are significant, inorganic photoconductor drums traditionally exhibit much higher durability—thereby resulting in a photoconductor having a desirable longer life. Inorganic photoconductor drums (e.g., amorphous silicon photoconductor drums) are ceramic-based, thus are extremely hard and abrasion resistant. Conversely, the surface of an organic photoconductor drums is typically comprised of a low molecular weight charge transport material, and an inert polymeric binder and are susceptible to scratches and abrasions. Therefore, the drawback of using organic photoconductor drums typically arises from mechanical abrasion of the surface layer of the photoconductor drum due to repeated use. Abrasion of photoconductor drum surface may arise from its interaction with print media (e.g. paper), paper dust, or other components of the electrophotographic image forming device such as the cleaner blade or charge roll. The abrasion of photoconductor drum surface degrades its electrical properties, such as sensitivity and charging properties. Electrical degradation results in poor image quality, such as lower optical density, and background fouling. When a photoconductor drum is locally abraded, images often have black toner bands due to the inability to hold charge in the thinner regions. This black banding on the print media often marks the end of the life of the photoconductor drum, thereby causing the owner of the printer with no choice but to purchase another expensive photoconductor drum. Photoconductor drum lives in the industry are extremely variable. Usually organic photoconductor drums can print between about 40,000 pages before they have to be replaced.
Increasing the life of the photoconductor drum will allow the photoconductor drum to become a permanent part of the electrophotographic image forming device. In other words, the photoconductor drum will no longer be a replaceable unit nor be viewed as a consumable item that has to be purchased multiple times by the owner of the ep printer. Photoconductor drums having an ‘ultra long life’ allow the printer to operate with a lower cost-per-page, more stable image quality, and less waste leading to a greater customer satisfaction with his or her printing experience. A photoconductor drum having an ultra ling life can be defined as a photoconductor drum having the ability to print at a minimum 100,000 pages before the consumer has to purchase a replacement photoconductor drum.
To achieve a long life photoconductor drum, especially with organic photoconductor drum, a protective overcoat layer may be coated onto the surface of the photoconductor drum. An overcoat layer formed from a silicon material has been known to improve life of the photoconductor drums used for color printers. However, such overcoat layer does not have the robustness for edge wear of photoconductor drums used in mono (black ink only) printers. A robust overcoat layer that improves wear resistance and extends life of photoconductor drums for both mono and color printers is desired.
Some overcoats are known to extend the life of the photoconductor drums. However one major drawback of these overcoats is that they significantly alter the electrophotographic properties of the photoconductor drum in a negative way. If the overcoat layer is too electrically insulating, the photoconductor drum will not discharge and will result in a poor latent image. On the other hand, if the overcoat layer is too electrically conducting, then the electrostatic latent image will spread resulting in a blurred image. Thus, a protective overcoat layer that extends the life of the photoconductor drum must not negatively alter the electrophotographic properties of the photoconductor drum, thereby allowing sufficient charge migration through the overcoat layer to the photoconductor surface for adequate development of the latent image with toner.